Carbon coated container for electrolytic condensers



June 29, 1937. s. BLOOMENTHAL 3 CARBON COATED CONTAINER FOR ELECTROLYTICCONDENSERS Filed May 2'7, 1933 Jidnsyfl Zaomenthal,

Patented June 29, 1937 PATENT OFFICE CARBON COATED CONTAINER FOR- ELEC-TROLYTIC CONDENSERS Sidney Bloomenthal, Merchantville, N. J assignor toRadio Corporation of America, a corporation of Delaware Application May27, 1933, Serial No. 673,162

10 Claims.

The present invention relates to electrolytic devices and, moreparticularly, to cathode structures for electrolytic condensers of thefluid electrolyte type and a method of producing the same.

In the manufacture of electrolytic condensers of the fiuid electrolytetype, various known film forming metals are utilized in making the filmforming anode. For example, metals such as tantalum, molybdenum,aluminum, and the like,

10 may be employed, although aluminum is preferable because it isreadily obtainable, easy to work and relatively inexpensive.

While aluminum is, therefore, highly desirable for the anode of anelectrolytic condenser of the character specified, it is not,ordinarily, suitable for the cathode structure of an electrolyticcondenser, such as the cathode-can or container, for the reason that ina filter circuit, the inverse cur-- rent causes a non-conductive filmtoform on the interior surface of the cathode-can. When such a film isformed on the cathode-can, the resistance of the condenser is increasedand the capacity thereof is lowered to the point where the condenser maybecome unfit for further use.

In order to obtain the advantages in the use of aluminum and like metalsfor the cathode structure of an electrolytic condenser, variousexpedients have been proposed heretofore to overcome the results of suchfilm formation on the cathode-can or container. Among such expedientsmay be mentioned the short-circuiting means disclosed in LilienfeldPatent 1,880,263, for example.

Likewise, cathode-cans or containers for electrolytic condensers of thefluid type, which are provided on their interior surface with anelectrodeposited surface of chromium, nickel, copper, or the like, toprevent the oxidizing of the container proper, when in use, are known.Containers formed entirely of copper, for example, are also known.However, containers of this character, while more satisfactory in use,are nevertheless subject to corrosion, are expensive to manufacture,and, when formed of copper, are more difficult to draw into the desiredshape.

Accordingly, it is an object of my invention to provide a cathodestructure for an electrolytic condenser which permits of the use ofdesired metals without being subject to the above-noted disadvantagesand objections, and whereby an electrolytic condenser may be providedwhose rated capacity will not change substantially over long periods ofuse through deterioration or change in the active cathode surface.

A further object of my invention is to provide an electrolytic condensercontainer having an inert, non-film forming, cathodic surface which willnot combine chemically with an electrolyte.

Another object of my invention is to provide a combined container andcathode electrode for an electrolytic condenser, the active surface ofwhich is provided with a non-metallic coating, whereby said containerand electrode may be constituted wholly of aluminum or a similar metalwhich is easily worked, low in cost, and which will not deteriorate whenin contact with an electrolyte.

A further object of my invention is to provide an electrolytic condensercathode-can or container and means whereby the formation of anon-conducting film on the cathode surface or surfaces thereof isprevented, said surface or surfaces being non-corroding andnon-oxidizing.

A further object of my invention is to provide an electrolytic condensercathode structure having a non-metallic film of conductive material as aprotective coating therefor, whereby the electrolyte is prevented fromcontacting with said structure.

A further object of my invention is to provide an electrolytic condenserunit of the character specified having a non-corroding insolublecathodic lining bonded to a surface thereof.

Another object of my invention is to provide an electrolytic condenserunit of the character specified wherein a low resistance, conductivefilm is formed on a cathode-can or container surface, said film being ofa character such that it will not crack, chip or become otherwisedetached jects and advantages thereof, will best be under stood from thefollowing description of a certain specific embodiment thereof, whenread in connection with the accompanying drawing, in

which Fig. l is a vertical sectional view, substantially full-size, of acathode-can or container embodying my invention,

Fig. 2 is a greatly enlarged fragmentary sectional view of a wall of thecathode-can or container shown in Fig. 1,

Fig. 3 is a sectional view taken on the line 3--3 of Fig. l and on thesame scale as Fig. 1.

Referring to the drawing, a cathode-can or container representing acathode structure, and generally indicated at H), comprises acylindrical container ll, preferably of aluminum, having a reduced endportion 12, an open end portion l3, and a film or coating It ofconductive material constituting the interior surface of the containerII.

In accordance with my invention, I first prepare a concentrated graphitesuspension which consists, preferably, of the following ingredients,acetone 137.8 cc., amyl acetate 125 cc., phenol formaldehyde resin 39.9grams, and 42.5 grams of 99% pure graphite, the acetone being thesolvent for the resin and the amyl acetate constituting the thinner.

In order that the graphite may be intimately mixed with the acetone andamyl acetate, I have found that this may be done, preferably, by millingthe solution in a suitable ball mill for an extended period of time, forexample, 24 hours more or less.

In the application of the graphite solution to the cathode-can orcontainer l0, after it has been suitably cleaned in a mild causticsolution, for example, the opening 15 in the reduced end portion l2thereof is first suitably corked or other- Wise closed. A quantity ofthe graphite suspension, sufficient to cover or coat the interiorsurface of the container H with a sufficient excess, is then spilled orpoured into the container I I, or, the solution may be otherwise appliedas by spraying the solution or by dipping the container into thesolution.

Immediately after a sufficient quantity of the graphite solution hasbeen placed in the container II and suitably distributed over its entireinner surface, the excess solution is drained off and the coating orfilm of the solution adhering to the container ll permitted to dry.

The container I l is then fired or baked, for example, for twenty-fourhours at a temperature of substantially 100 degrees centigrade to hardenthe adhering graphite film or coating whereby a non-porous, lowresistance conductive film or lining is formed within the container ll.

As hereinbefore stated, the container l I with the graphite film orcoating H applied to its entire interior surface, is first subjected toa temperature of 100 degrees centigrade so that the said film or coatingwill bake slowly to obviate blistering or cracking of the said film orcoating.

After the film or coating has been baked slowly at substantially thetemperature specified above, it is, preferably, subjected to a furtherbaking temperature much higher than the first, for example 1'70 degreescentigrade for approximately two hours, whereby the resin in thegraphite film or coating I4 is thoroughly polymerized or set.

While I have specified acetone as the solvent for the phenolformaldehyde resin, and amyl acetate as the medium for thinning thesolution resulting from the admixture of the resin to the acetone, it isto be expressly understood that I may substitute, for example, ethylalcohol for the acetone and butyl or ethyl acetate for the thinner.Similarly, I may also substitute other binders for the phenolformaldehyde resin as, for example, resin compounds such as shellac forexample, or, certain esters such as nitrc-cellulose, for example, mayalso be employed.

From a consideration of the above, it will be readily apparent that myimproved cathode-can or container for electrolytic condenser of thefluid type provides a low resistance path from the cathode-can orcontainer ll proper through the film or coating Hi to the electrolytewhen a completed condenser, as herein specified, is in use. For example,if a cathode-can or container, constructed in accordance with myinvention, is filled with mercury to test the resistance of acathode-can or container formed in accordance with my invention, thetotal resistance across the coating from the container proper to themercury would be less than 3 ohms for a container such as shown inFig. 1. Moreover, the power factor and internal resistance of such acondenser is not changed by reason of the conductive film or coating onthe interior surface of the container.

In carrying out my invention, the use of graphite is preferable becauseit is readily obtainable in very pure form. However, it is to beunderstood that a very pure lamp black or similar forms of lowresistance carbon or, a colloidal graphite such as Aquadag mixed with acolloidal phenol formaldehyde resin suspension, may be readilysubstituted for the graphite with equally satisfactory results if suchsubstitutes are free from V traces of foreign materials.

The more common foreign materials to be guarded against are chlorides,sulphates, sulphides, nitrates, and similar acid ions, since thecombination of such materials with aluminum gives rise to products whichhydrolize readily and cause disintegration of the anode and its aluminumoxide film. Hydrolysis oi this character is typical of salts which maybe formed by the reaction of a weak base (aluminum hydroxide) with astrong acid (HCl, H2804, HNOa, etc.).

I claim as my invention:

1. A cathode structure for electrolytic condensers having a non-metallicimporous, hard conductive film on an active surface thereof.

2. A cathode structure for electrolytic condensers comprising acontainer having a film or coating of non-metallic conductive materialbonded to the interior active surfaces thereof.

3. A cathode can container for electrolytic condensers having a film ofinert non-metallic conductive material bonded to the interior surfacethereof.

4. In combination, a container providing a cathode unit for anelectrolytic condenser, and means providing an inert coating of lowresistance non-metallic conductive material bonded to an active cathodesurface of said container.

5. A cathode for an electrolytic condenser comprising a can having asmooth adherent film of imporous, hard non-metallic conducting materialon the interior surface thereof.

6. As an article of manufacture, a cathode for an electrolytic condenserof the fluid electrolyte type comprising a can having a non-metallic,inert cathodic surface of imporous conductive material.

7. As an article of manufacture, a cathode for an electrolytic condenserof the fluid electrolyte type comprising a container can having aninert, non-metallic, non-frangible lining of imporous conductivematerial bonded to an interior surface of said container can.

8. As an article of manufacture, a cathode for an'electrolytic condenserof the fluid type comprising a container having an inert, insoluble filmof non-metallic conductive material bonded in: substantially puregraphite and polymerized resin.

10. A cathode can container for electrolytic condensers having a film ofinert conductive material bonded to the interior surface thereof, said 5film comprising substantially pure graphite and polymerized resin.

SIDNEY BIDOLIENI'HAL.

